A new high-frequency audiometer has been developed with NIH/NINCDS support. The audiometer uses digital signal processing to calibrate each ear individually, and provides accurate estimates of the sound pressure level at the apex of the auditory canal. The new audiometer can serve in establishing valid audiometer standards for the normal population and for reliable determination of high-frequency hearing loss, an early warning of the long term effects of exposure to noise or ototoxic substances. Calibration is effected by analysis of features of the spectrum of an impulse reflected from the eardrum. The applicants plan to transform the present experimental prototype into a product that is compact, moderate in cost and simple to use. Such a device would be responsive to the expressed needs of audiological clinics and of value in research aimed at discovery of ototoxic processes. Product development requires detailed theoretical study of the acoustics of the ear canal, of the device, and of their interaction; design and construction of signal processing circuitry suitable for quantity production; and, audiometric testing to validate each step of engineering design.